Method of forming a belt structure in a tyre, in particular for motorcycle wheels

ABSTRACT

Formation of a bell structure ( 2 ) takes place by laying down, directly on the carcass structure ( 3 ) of a tyre being processed ( 1 ), a laying layer ( 16 ) formed of a continuous strip-like element ( 16 ) of elastomer material directly coming from an extrusion die. The strip-like element ( 16   a ) has a differentiated thickness at its opposite edges to give rise to circumferential grip recesses ( 18 ) on the laying layer ( 16 ). Then, on the laying layer ( 16 ) a primary belt strip ( 6 ) is formed which is obtained by winding up of a continuous bare cord into coils ( 6   a ) disposed in axial side by side relationship. A cord of the high starting elongation type is preferably employed and it is wound up substantially in the absence of tensioning. A covering layer ( 19 ) made in the same manner as the laying layer ( 16 ) can be subsequently laid down on the primary belt strip ( 6 ).

[0001] The present invention relates, in a general aspect thereof, to amethod of building a belt structure in a tyre, in particular formotorcycle wheels.

[0002] Tyre building for vehicle wheels involves formation of a carcassstructure essentially made up of one or more carcass plies substantiallyshaped in a toroidal configuration and having their axially oppositeside edges in engagement with respective annular reinforcing structuresincorporating circumferentially inextensible annular elements, usuallyreferred to as “rings”.

[0003] Applied to the carcass structure, at a radially external positionthereof, is a belt structure comprising one or more belt strips in theform of a closed ring, essentially made up of textile or metallic cordswhich are suitably oriented with respect to each other and to the cordsbelonging to the adjacent carcass plies.

[0004] In addition, a tread band is applied to the belt structure at aradially external position thereof, which tread band is usually made upof a strip of elastomer material of appropriate thickness.

[0005] To the aims of the present specification it should be pointed outthat by the term “elastomer material” it is intended a rubber blend inits entirety, that is the assembly made up of at least one base polymersuitably amalgamated with reinforcing fillers and/or process additivesof various types.

[0006] Finally, a pair of sidewalls is applied to the opposite sides ofthe tyre being formed, each of said sidewalls covering a side portion ofthe tyre included between a so-called shoulder region, located close tothe corresponding side edge of the tread band, and a so-called beadlocated at the corresponding annular reinforcing structure.

[0007] While tyres for cars or trucks are characterised by asubstantially flattened cross-section outline at the tread band, tyresfor motorcycles are distinguishable due to their marked transversecurvature or bending, usually defined by the particular ratio valuebetween the distance of the tread centre from the line passing throughthe opposite side extremities of the tread itself, measured at theequatorial plane of the tyre, and the distance measured along the tyrechord between said extremities. In tyres for two-wheeled vehicles thevalue of the bending ratio generally is at least as high as about 0.15and it is usually in the order of 0.3 in the case of rear tyres, andeven higher, until 0.45 in the case of front tyres, against a valueusually smaller than 0.05 in tyres for motor-vehicles.

[0008] Formation of the belt structure is usually accomplished on anauxiliary metal drum, a “comb drum” for example or a smooth drum, onwhich one or more belt strips are formed and radially superposed todefine a so-called belt ring, to which the tread band is then applied.In building of tyres having a high transverse curvature, formation of atleast one belt strip is provided which is obtained by circumferentiallywinding up at least one textile or metallic and optionally rubberizedcord into a plurality of coils disposed in axial side by siderelationship according to a winding angle of substantially zero valuewith respect to the equatorial plane, on expandable sectors of theauxiliary drum already in a radially expanded position and convenientlyshaped so as to correspond to the curvature outline of the tyre.

[0009] After, carrying out application of the tread band, the beltring-tread band assembly is picked up from the comb drum to be coaxiallyfitted on the carcass structure previously made in the form of acylindrical sleeve on a building, drum. The carcass structure is thensubmitted to a conformation step by radial expansion of the carcassplies in a toroidal outline, concurrently with axial approaching of theannular reinforcing structures. During this step, the carcass pliesadhere to the inner surfaces of the belt ring previously disposed incoaxial relationship around the carcass sleeve.

[0010] In the case of a belt structure having cords oriented with asubstantially zero angle relative to the equatorial plane of the tyrebeing formed, it is not possible to lay down the cords on a cylindricalsurface and thus give said surface a toroidal conformation, because saidcircumferential orientation of the cords does not enable elongation ofthe latter to the extent required by conformation, in motorcycle tyres.Therefore the cord must be formed into spirals directly on the outlineof the carcass or the drum having already reached a toroidalconformation.

[0011] Up to now it has been found it convenient, for process reasons,not to wind up one single cord, but to simultaneously wind up severalcords in the form of a strap. Exactly straps are ribbons of elastomermaterial incorporating two to ten cords at least partly. Actually,laying down of bare cords with a substantially zero angle relative tothe equatorial plane of the tyre would lead to slipping of same out ofthe desired position during the winding step on the toroidal outline,exactly due to their precarious position.

[0012] Therefore forming the cords into a strap has the function ofensuring maintenance of the desired position by the cords during all thetyre preparation steps.

[0013] For the above aim in document EP-A-0 718 122 in the name of thesame Applicant, application of a thin layer of elastomer material(laying layer) filled with aramid fibres or the like is suggested beforewinding up of the coils. In more detail, this layer is formed by windingup on the auxiliary drum, a thin blend sheet obtained from calendering,of a thickness included by way of example between 0.075 and 0.5 mm, andof a width substantially corresponding to the width of the beltstructure to be obtained.

[0014] The Applicant has found it useful to utilise, in making the beltlayer as above described, cords of the so-called high startingelongation type, for example metallic cords of the HE or HI type, ascommonly identified in the field, or elastic textile cords.

[0015] The abbreviation HE means “High Elongation” and points out thatwinding of the strands in the cord and the wires in each strand iscarried out in the same direction (according to the so-called Lang's Layconstruction).

[0016] In addition, winding is of such a nature that small movements ofthe strands relative to each other are allowed. In this way the finishedcord substantially acquires a particular load-elongation curve of itsown which has an important change of slope, usually called “knee”, inthe elongation values on achieving a given load. In particular, thestarting line of the curve shows very important elongations for smallload variations, and is connected through the knee to the final line ofthe curve showing very small elongations for important load variations.

[0017] A cord of this type is described in document EP-B-461 646, in thename of the same Applicant. The centre line value of the knee conditionsthe correct building and moulding of the tyre and, to this aim, itusually corresponds to an elongation included between 0.4% and 1%.

[0018] The abbreviation HI identifies cords in which at least one of thewires is deformed due to bending along its longitudinal extension, so asto create gaps where rubber penetrates into the cord. This type of cordhas an intermediate behaviour (defined by the curve load/elongation)between that of the cords in opposite directions (of the Regular Laytype) and that of the cords in the same direction (of the Lang's Laytype).

[0019] As an alternative to the metallic cords, use of elastic textilecords is provided, made of Kevlar (polyethylene terephthalate) forexample. These cords are made up of bundles of filaments of organicmaterial, suitably twisted so as to achieve behavioural features similarto those of the above described metallic cords.

[0020] In accordance with the present invention, the applicant has foundit advantageous to make said laying layer by winding up, either directlyon the carcass structure or on a rigid support element, such as theassembly of convex sectors of a rigid and dismountable comb drum or atoroidal drum the radially external surface of which conforms in shapeto the radially internal surface of the tyre being processed, at leastone continuous strip-like element of elastomer material, preferablydirectly fed from an extruder head, in order to form a plurality ofcoils disposed axially close to each other so as to cover the wholewidth of the belt structure to be formed.

[0021] In the following, unless differently stated, by the term “supportmandrel” it is intended the carcass structure or rigid support elementon which the strip-like element is wound up in accordance with theinvention.

[0022] In fact, it has been found that such a building method can beadvantageously embodied in modern process conceptions aiming ateliminating or at least limiting the requirement of producing andstoring semifinished products, as' described in document EP-A-0928680 inthe name of the same Applicant, for example. In particular, the methodin reference makes it advantageously possible to meet the requirement ofimmediately differentiating the geometrical and structural features ofthe components of the belt structure in connection with the size and/ormodel of the tyre being processed.

[0023] The above stated results and still others that will become moreapparent in the course of the present description are achieved inaccordance with the present invention by a method of building a beltstructure of a tyre, in particular for two-wheeled vehicles, comprisingthe steps of:

[0024] forming at least one laying layer of elastomer material on anouter surface of a support mandrel conforming in shape to an outersurface of a carcass structure of a tyre being processed;

[0025] helically winding at least one continuous bare cord on saidlaying layer, to form a plurality of coils with said cord which aredisposed axially in side by side relationship,

[0026] characterized in that the laying layer is formed by laying downat least one continuous strip-like element of elastomer material in theform of helical coils axially distributed on the outer surface of thesupport mandrel.

[0027] Further features and advantages will be best understood from thedetailed description of a preferred but not exclusive embodiment of amethod of building a belt structure for tyres, in particular fortwo-wheeled vehicles, and a tyre to be obtained by said method, inaccordance with the present invention. This description will be set outhereinafter with reference to the accompanying drawings given by way ofnon-limiting example, in which:

[0028]FIG. 1 is a fragmentary perspective and split view of a tyre formotorcycles provided with a belt structure built in accordance with thepresent invention;

[0029]FIG. 2 is a fragmentary section taken in a radial plane of thetyre in FIG. 1 introduced into a vulcanization mould;

[0030]FIG. 3 shows the tyre in FIG. 2 during an end step of the mouldingand vulcanization process within the mould;

[0031]FIG. 4 shows the cross-section outline to an enlarged scale of astrip-like element of elastomer material to be used for carrying out theprocess in question;

[0032]FIG. 5 shows the cross-section outline to an enlarged scale of analternative embodiment of the strip-like element in FIG. 4.

[0033] With reference to the drawings, a tyre, in particular fortwo-wheeled vehicles, having a belt structure 2 built in accordance withthe present invention has been generally identified by reference numeral1.

[0034] The belt structure 2 is circumferentially applied to a carcassstructure 3 which, in this specific case, has two carcass plies 4 of asubstantially toroidal configuration in engagement by their oppositecircumferential edges with a pair of annular reinforcing structures 5(only one of which is shown in the drawings), each of them beinglocated, when the tyre has been finished, in the region usuallyidentified by “bead”.

[0035] The belt structure 2 comprises at least one primary belt strip 6made up of one or more continuous parallel cords wound up into coils 6 adisposed axially close to each other and laid down with a substantiallyzero angle relative to the equatorial plane of the tyre, as well as, inthe present case, of auxiliary belt strips 7 a, 7 b comprising cordsthat are disposed obliquely according to respectively crossedorientations, placed at a radially internal position with respect to theprimary belt strip 6. Circumferentially superposed on the belt structure2 is a tread band 8 in which longitudinal and/or transverse grooves 8 aare formed following a moulding operation carried out concurrently withtyre vulcanization, which grooves are disposed so as to define a desired“tread pattern”.

[0036] The tyre further comprises a pair of so-called “sidewalls” 9laterally applied to the carcass structure 3 on opposite sides thereof.

[0037] In the present case the carcass structure 3 is coated on itsinner walls with a so-called liner 10 essentially consisting of a layerof air-tight elastomeric material adapted to ensure a hermetic seal tothe tyre when inflated.

[0038] The present invention can be advantageously put into practicewithin the context of a building method according to which, except forthat which is described in more detail in the following of the presentspecification, assembling of the above listed components as well asproduction of one or more of them, is preferably obtained following theteachings proposed in document EP-A-976536 in the name of the sameApplicant. As provided in the above mentioned document, each componentof tyre 1 is obtained by laying down on a toroidal support 11 (onlydiagrammatically shown) the shape of which matches that of the innerconformation of the tyre, one or more elements obtained from anelongated semifinished product continuously fed in the vicinity of thetoroidal support itself.

[0039] The toroidal support 11, of a cross-section outline having abending ratio at least as high as 0.15, in conformity with the bendingratio of tyre 1 to be made, can have reduced sizes with respect to thoseof the finished tyre, of a linear measure value preferably includedbetween 2% and 5%, taken by way of example, along the circumferentialextension of the support itself at an equatorial plane X-X thereof whichis coincident with the equatorial plane of tyre 1.

[0040] In more detail, liner 10 can be obtained by winding up acontinuous strip-like element of appropriate elastomer material on theouter surface of the toroidal support 1 to form a plurality of coils 10a disposed in axial side by side relationship and/or radialsuperposition, so as to define a continuous layer adapted to integrallycoat the inner surface of tyre 1.

[0041] Each carcass ply 4 can be in turn made up of a plurality oflengths 12, 13 circumferentially distributed around the geometric axisof tyre 1 and each extending in a U-shaped configuration to define twoside portions 12 a, 13 a spaced apart from each other in an axialdirection, and a crown portion 12 b, 13 b extending at a radiallyexternal position between the side portions 12 a, 13 a. In more detail,the presence of a first series of lengths 12 and a second series oflengths 13 is preferably provided and they are laid down on the toroidalsupport 11 in two successive steps and have the respective side portions12 a, 13 a axially spaced apart from each other by interposition of oneor more of the construction components belonging to the annularreinforcing structures 5. Lengths 12, 13 belonging to the first andsecond series respectively can be distributed according to acircumferential pitch substantially corresponding to their width to formtwo separate carcass plies. For tyres intended for use in motorcycles itis however preferably provided that, as shown in FIG. 1, the lengths 12,13 of each series should be distributed according to a circumferentialpitch corresponding to a multiple of their width, so that the crownportions 13 b of the lengths 13 belonging to the second series are eachinterposed between the crown portions 12 b belonging to two consecutivelengths of the first series 12, to form a single carcass ply 4altogether.

[0042] Depending on requirements, lengths 12, 13 belonging to the firstand second series can be laid down in planes that are radial to therotation axis of the toroidal support 11, or offset in parallel relativeto said radial plane, as described in document WO 00/38906 in the nameof the same Applicant, to obtain a respectively crossed orientation oftheir side portions 12 a, 13 a, keeping the crown portions 12 b, 13 boriented perpendicular to a circumferential direction. Deposition can bealso carried out in an inclined orientation relative to thecircumferential extension direction of the toroidal support 11, to givethe crown portions 12 b, 13 b a desired inclination, not exceeding 15degrees for example, relative to said circumferential direction.

[0043] Each of the annular reinforcing portions 5 preferably comprisesan annular anchoring insert 14 which is substantially inextensible in acircumferential direction, located close to the radially internal edgeof the carcass structure 3, and a filling insert 15 of elastomermaterial, tapering radially away from the anchoring insert 14.

[0044] The annular anchoring insert 14 is preferably obtained by windingup of an elongated element directly against the side portions 12 a oflengths 12 belonging to the first series, so as to form a plurality ofcoils that are radially superposed in succession. The filling insert 15can be in turn directly formed in contact with the annular anchoringinsert 14, for instance by applying, possibly in several coils disposedin axial side by side relationship and/or radial superposition, acontinuous strip of appropriate elastomer material coming out of anextruder disposed close to drum 11.

[0045] To the aims of the present specification it is pointed out thatby “extruder” it is intended that part of the extrusion apparatus thatis also identified in the particular field by the term “extruder head”,provided with a so-called “die” passed through by the product beingprocessed at an opening shaped and sizes so as to meet the geometric anddimensional features to be given to the product itself.

[0046] The anchoring insert 14 and filling insert 15 are preferablyapplied before deposition of lengths 13 belonging to the second series.An auxiliary anchoring insert 14 a can be subsequently formed againstthe side portions 13 a of lengths 13 belonging to the second series,previously laid down in superposed relationship on the insert 14 andfilling 15.

[0047] Subsequently to deposition of lengths 13 belonging to the secondseries, formation of the belt structure 2 takes place.

[0048] In the preferential embodiment herein described in which aspreviously said, building of individual components directly on the tyrebeing processed is provided, the belt structure 2 is produced directlyon the carcass structure 3 that, together with the toroidal support 11,in this case also performs the function of support mandrel for formationof the individual components of the belt structure 2 itself.

[0049] However, the process in accordance with the invention can beadvantageously put into practice also in the context of building methodsin which the belt structure 2 is produced separately from the carcassstructure 4, to be joined to the latter in a subsequent step. In thiscase, the operating steps aiming at making the individual components ofthe belt structure 2 can be carried out on the outer surfaces of a drumor other appropriate support mandrel, conveniently shaped so as' tomatch the outer surface of the carcass structure 4 with which the beltstructure 2 will be associated.

[0050] For the purpose of building the belt structure 2 it is providedthat after possible application of the auxiliary belt strips 7 a, 7 bformation of which can be carried out in any convenient manner, theprimary belt strip 6 should be formed by winding up of the continuouscord coils 6 a on the carcass structure 3.

[0051] Formation of the primary belt strip 6 is advantageously precededby formation of at least one laying layer 16 of elastomer materialadapted to constitute an attachment substrate adapted to promote asteady positioning of the individual coils 6 a on the tyre beingprocessed.

[0052] The laying layer 16 is advantageously formed by laying down atleast one continuous strip-like element 17 in the form of helical coils16 a oriented in a substantially circumferential direction and axiallydistributed on the outer surface of the carcass structure 4, at thecrown portions 12 b, 13 b of lengths 12, 13. In more detail, thecontinuous strip-like element 17 is provided to be laid down on thecarcass structure 4 concurrently with its extrusion from an extruder,and formation of the primary belt strip 6 is provided to be preferablycarried out immediately after completion of the laying layer 16.

[0053] By operating in the above described manner, there is an advantagebecause the cord coils 6 a are formed on the laying layer 16 when theelastomer material constituting said layer is still relatively hot, justas an indication at a temperature at least as high as 35° C., because itstill keeps most of the heat generated during the extrusion process. Inthis way adhesion of the individual cord coils 6 a to the laying layer16 is promoted, without addition of heat by means of external devicesbeing required for the purpose.

[0054] In addition, appropriate grip recesses 18 are provided to bedefined on the laying layer 16 having an average thickness included,just as an indication, between 0.2 mm and 1 mm, preferably correspondingto 0.7 mm, said recesses being suitably oriented in the same windingdirection as the cord coils 6 a, to further promote steady positioningof same. To this aim, as seen in FIG. 4, the continuous strip-likeelement 17 can be advantageously formed, using a suitably shapedextruder head, with at least a convex outer surface 17 a facing awayfrom the outer surface of the carcass structure 4 to which thestrip-like element itself is applied. Alternatively, as viewed from FIG.5, the continuous strip-like element 17 can also have a lenticularcross-section outline, with two convex surfaces 17 a turned towardsrespectively opposite sides. Both embodiments shown in FIGS. 4 and 5enable formation of the grip recesses 18 to be caused between each coil16 a and the coils adjacent thereto, directly following winding of thecontinuous strip-like element 17 according to a spiralling pitch thatcan be included, just as an indication, between 1 mm and 10 mm, andpreferably corresponding to the width of the strip-like element itself.

[0055] A similar effect can be achieved by use of a strip-like element17 of a constant thickness, wound up according to a spiralling pitchsmaller than its width, so as to cause a more or less marked overlappingof each coil 16 a on the previously formed coil.

[0056] The laying layer 16 made as above described is surprisingly ableto ensure steadiness of positioning of the cord coils 6 a even when, asprovided in a preferential embodiment of the invention, the primarystrip 6 of the belt structure 2 is formed using a completely orsubstantially rubber-free cord. This feature is particularlyadvantageous when the method, as in the described example, applies to agreatly automated building process in which maximum simplification ofthe installation is required along with a great production flexibility.

[0057] The possibility of using bare cords, i.e. rubber-free cords, infact eliminates the requirement of arranging calendering and/orextrusion apparatuses adapted to carry out cord rubberizing. Alsogreatly facilitated is replacement of the type of cord used in theproduction process, without the need for long and/or particularlycomplicated interventions to be carried out on the production plant.

[0058] It is also to be pointed out that, during the cord rubberizingprocess aiming at forming the strap, the cord is submitted to tensionsthat modify the operating features thereof (elongation to low loads)impairing regularity and evenness of the subsequent expansion of thebelt structure within the vulcanization mould, as depicted in moredetail in the following in connection with a similar phenomenon that canbe found during the deposition step of the belt structure itself.

[0059] In particular, to the aims of the formation of the primary beltstrip 6 cords made of steel of the type having a high startingelongation can be advantageously used, the tensile behaviour of whichrepresented on a load/elongation curve is characterized by the presenceof a starting line of low slope, which is an index of high extensibilityfor low loads, followed by a final line of marked slope, which is anindex of high toughness for loads higher than a predetermined value. Inparticular, preferably used are cords in which the transition region(knee) between the starting line and final line of the load/elongationcurve develops around an elongation in the order of 0.7%, for instancecords the size of which is 3×3×0.175.

[0060] The Applicant has noticed that if the primary belt strip 6 shouldbe formed following the teachings of the known art, it would benecessary to give the cord being wound an important tensioning in orderto avoid undesirable displacements of the individual coils 6 a takingplace as a result of the marked surface bending of the carcass structure4 or other type of support mandrel therein used.

[0061] This tensioning would modify the operating features (elongationto low loads) of the cord thereby impairing regularity and evenness ofthe subsequent expansion of the belt structure within the vulcanizationmould.

[0062] The presence of the laying layer 16, on the contrary, enables asteady positioning of the individual coils 6 a to be ensured, even inthe absence of tensioning on the cord or other thread-like element usedduring the winding step, or in the presence of a tensioning of a veryreduced amount.

[0063] In particular, it is advantageously possible to carry out windingof the cord giving the same a tensioning not exceeding 1500 grams,preferably of 1000 grams, more preferably of 500 grams, or in any caseof such an amount that an elongation not exceeding 0.3% is imposed to acord of the type preferably used in accordance with the invention.

[0064] As will be further specified in the following, this aspect makesit possible to exploit in an optimal manner the features typical of thecords preferably employed in accordance with the present invention.

[0065] Winding of the cord for making coils 6 a can take place accordingto a constant spiralling pitch of a value at least as high as thediameter of the cord used, or a varying pitch having an increasing valueon coming close to the equatorial plane of the tyre as described indocument EP-A-808730 in the name of the same Applicant, for example.

[0066] When formation of the primary belt strip 6 has been completed, atleast one covering layer 19 of elastomer material is preferably formedin radial superposed relationship with the primary strip itself. Theprimary layer 19 can be obtained, in the same manner as described withreference to the laying layer 16, by laying down at least one secondstrip-like element of elastomer material in the form of axiallydistributed helical coils 19 a, said second element being preferablylaid down concurrently with its extrusion from an extruder head.

[0067] Then the tread band 8 and sidewalls 9, that can be obtained inany manner convenient for a person skilled in the art, are applied tothe belt structure 2.

[0068] Tyre 1 thus built now lends itself to be submitted, afterpossible removal from support 11, to a moulding and final vulcanizationprocess, carried out within one mould diagrammatically shown and denotedat 20 in FIGS. 2 and 3. During the moulding and vulcanization processpressing of tyre 1 against the inner walls of mould 20 is imposed, byeffect of the pressure of the steam or other pressurized fluid directlyintroduced into the tyre or into an inflatable bladder within themoulding cavity. Following such a pressing action, permeation of theelastomer material between the cord coils 6 a forming the primary beltlayer 6 is obtained as well as within the cord itself. Coils 6 a and theindividual cord strands are therefore intimately incorporated into theelastomer material forming the laying layer 16 and the possible coveringlayer 19, causing evacuation through the material porosity of airbubbles possibly formed during application of the covering layer 19and/or the tread band 8. This effect can be clearly inferred bycomparing FIGS. 2 and 3, in which the size of said air bubbles has beenintentionally exaggerated.

[0069] In more detail, in the preferential embodiment shown, tyre 1 isprovided to be introduced into mould 20 together with the toroidalsupport 11, to carry out the moulding and vulcanization process asdescribed in document EP-A-9765EE, in the name of the same Applicant.

[0070] By effect of pressure of the steam admitted to within mould 20,the belt structure 2 along with the other components of tyre 1 closethereto are provided to be submitted to a radial expansion, as clearlyshown in FIG. 3, where the inner surface of tyre 1 is clearly spacedapart from the outer surface of the toroidal support 11.

[0071] This radial expansion that greatly facilitates the mouldingprocess of tyre 1 is made possible or at all events greatly promoted bythe residual capability of extension of the cord used in forming thecircumferential coils 6 a. In fact, the cord is adapted to lengthenthereby backing up the circumferential extension increase resulting fromradial expansion until reaching of a point (an elongation value)included within the transition line (knee) between the starting line andthe final line of the load/elongation curve.

[0072] The radial capability of extension of tyre 1 is conditioned bythe capability of extension or stretchability of the cord. Therefore,achievement of two targets appears to be advantageous, i.e. that ofusing bare cords which therefore are not submitted to tensions duringthe process of incorporating them into a strap, and that of carrying outwinding of the circumferential coils 6 a without imposing an excessivetensioning to the cord therein used because in the presence of excessivetensioning the residual stretchability of said cord during the mouldingand vulcanizing process would be greatly reduced if not cancelled.

[0073] The present invention achieves important advantages.

[0074] The method of the invention in fact lends itself to drasticallylimit previous arrangement of semifinished products for building thetyre even when there is a requirement for producing small amounts oftyres having different construction features. In this connection itshould be noted that the laying layer 16 and the possible covering layer19 can be formed of any size in width and/or thickness, using one andthe same continuously extruded strip-like element.

[0075] The possibility of using rubber-free cords (i.e. cords that arenot even partly incorporated into a strap) for formation of the primarybelt strip 6 enables an immediate replacement of the type of cord used,without any interventions on the calendering and/or extrusion apparatusthat, on the contrary, would be necessary should the cord be of therubberized type. In addition, as already pointed out above, submittingthe cord to tensions that would be harmful to the following steps of theproduction process is avoided.

[0076] Winding of the cord coils 6 a on a still hot elastomer materiallaid down so as to create circumferential recesses 18 ensures steadinessof the coils without being obliged to resort to tensioning of the cordduring the winding operation.

[0077] Thus it is possible to fully exploit the cord features in thesubsequent moulding and vulcanization process of the tyre, without theoccurrence of undesirable contacts between the cords of the beltstructure 2 and the cords of the carcass structure 3, due to radialexpansion of the carcass structure in the absence of a correspondingexpansion of the belt structure itself. In addition, the process can beadvantageously carried out directly on the carcass structure of the tyrebeing built.

1. A method of forming a belt structure in a tyre, comprising the stepsof: forming at least one laying layer (16) of elastomer material on anouter surface of a support mandrel conformed in shape to an outersurface of a carcass structure (4), of a tyre being processed; helicallywinding up at least one continuous bare cord on said laying layer (16),to form a plurality of coils (6 a) with said cord which are disposedaxially in side by side relationship, characterized in that the layinglayer (16) is formed by laying down at least one continuous strip-likeelement (17) of raw elastomer material in the form of helical coils (16a) axially distributed on the outer surface of the support mandrel.
 2. Amethod as claimed in claim 1, wherein said continuous strip-like element(17) is laid down on the outer surface of the support mandrel (4, 11)concurrently with its extrusion from an extruder head.
 3. A method asclaimed in claim 1, wherein during the winding step the laying layer(16) has a temperature greater than 35° C.
 4. A method as claimed inclaim 1, wherein deposition of the laying layer (16) gives rise to griprecesses (18) for said continuous thread-like element (6 a).
 5. A methodas claimed in claim 4, wherein said grip recesses (18) are formedaccording to the same winding direction as the cord coils (6 a).
 6. Amethod as claimed in claim 1, wherein the continuous strip-like element(17) is formed with at least one convex outer surface (17 a) facing awayfrom the outer surface of the support mandrel (4, 11).
 7. A method asclaimed in claim 4, wherein winding of said continuous strip-likeelement (17) having at least one convex outer surface gives rise to saidgrip recesses (18) between coils (16 a) disposed axially close to eachother formed by said continuous strip-like element.
 8. A method asclaimed in claim 1, wherein said support mandrel is at least partlydefined by the carcass structure (3) of the tyre (1).
 9. A method asclaimed in claim 8, wherein said support mandrel further comprises arigid toroidal support (11) the shape of which matches that of an innersurface of said carcass structure (3).
 10. A method as claimed in claim1, wherein said cord is a cord having a high starting elongation.
 11. Amethod as claimed in claim 10, wherein said cord is a cord having aconformation of the Lang's lay type.
 12. A method as claimed in claim10, wherein said cord is a cord with at least one wire deformed alongits longitudinal extension.
 13. A method as claimed in claim 10, whereinsaid cord is an elastic textile cord.
 14. A method as claimed in claim10, wherein during said winding step said cord is submitted to atensioning to which a percent elongation of the cord not exceeding 0.3%corresponds.
 15. A method as claimed in claim 10, wherein during saidwinding step said cord is submitted to a tensioning not exceeding 1500grams.
 16. A method as claimed in claim 15, wherein tensioning does notexceed 1000 grams.
 17. A method as claimed in claim 16, whereintensioning does not exceed 500 grams.
 18. A method as claimed in claim1, wherein after the winding step, the step of forming at least onecovering layer (19) of elastomer material at a radially externalposition relative to the cord is carried out.
 19. A method as claimed inclaim 18, wherein formation of said covering layer (19) precedes a stepof applying a tread band (8) to said belt structure (2).
 20. A method asclaimed in claim 18, wherein formation of the covering layer (19) iscarried out by laying down at least one second continuous strip-likeelement of elastomer material in the form of helical coils (19 a)axially distributed on the outer surface of the support mandrel (4, 11).21. A method as claimed in claim 18, wherein the second continuousstrip-like element is laid down on the outer surface of the supportmandrel (4, 11) concurrently with its extrusion from an extruder head.22. A method as claimed in claim 10, further comprising the step ofcausing permeation of the elastomer material forming the laying layer(16) between the coils (6 a) formed by said cord, concurrently with aradial expansion imposed to the belt structure (2) during a finalmoulding and vulcanization process of the tyre (1).
 23. A method asclaimed in claim 10, further comprising the step of causing permeationthrough said cord of the elastomer material forming the laying layer,concurrently with a radial expansion imposed to the belt structure (2)during a final moulding and vulcanization process of the tyre (1).
 24. Amethod as claimed in claim 1, wherein said tyre is a tyre formotorcycles.